1. Technical Field
The invention relates to the art of machining internal combustion engine cylinder heads and, more particularly, to the art of grinding or coring valve seats and valve guides for such heads.
2. Description of the Prior Art
Valve seat machining or coring is a well established art which consistently has used a tool pilot fitting into a completed guide opening (for the stem of a valve associated with the valve seat) thereby to align the cutting tool for concentrically machining or reboring the valve seat (see U.S. Pat. Nos. 3,674,375; 3,764,204; 4,147,462; and 4,545,706). U.S. Pat. No. 4,545,706, in particular, compounds the problem of alignment by using the wrong sequence and aligning the seat somewhat independent of the guide bore. This patent sizes the guide bore and locates its axis prior to independently sizing and locating the valve seat. Although a reaming tool for the valve guide and a cutting tool for the valve seat are mounted on a common spindle head, the head articulates about a universal joint to allow the reaming tool to complete boring of the guide bore in advance of the valve seat. Thus, when cutting the valve seat, a bearing cradle aligns the head eliminating guidance by the guide bore.
Due to the surface finish of such reboring, cutting or reaming action, a facing operation must be carried out to grind the valve seat, and sometimes the guide bore, to a tolerable surface finish (see German patent No. 876,959; U.S. Pat. Nos. 1,906,263; 1,981,269; 2,150,621; and 2,363,384).
Unfortunately, all of the above disclosures have not only been limited by the ability to machine only the valve seat in one pass of the tool holder and to machine the guide bore in another separate pass, but also have been limited by the relatively rough shape of the wrought metal seat and bore inserts, requiring cutting of the final seat or bore surface to general size and location followed by finish machining of such surfaces to complete the sequence. A large amount of metal material must be removed in the first stage of the sequence of this art, necessitating slower machining speeds (both rotary and feed) for less than optimum productivity. The valve seat obtains only a macroscale alignment with respect to the valve guide (macroscale is defined herein to mean a dimensional tolerance where the units of dimensional difference are no closer than 0.01 inch). To reduce wear and to deploy lubrication better, there is a great need for closer tolerances than exist on a macroscale.
Deploying lubrication better is a related problem. Fully dense wrought metal inserts, used by such art for the seat and stem guide sleeve, are of a harder material than the remainder of the cylinder head but suffer from replenishment of the lubricant throughout the totality of the interfacing surfaces. There is a lack of optimal lubrication at the interface between the moving valve head and the fixed seat insert, and a lack of optimal lubrication in the space or gap between the moving valve stem and the fixed guide sleeve. The use of multiple stages of machining of the same surfaces also eliminates any hope for controlled porosity in such surfaces.